Below is the link to a gizmo on ExploreLearning focusing on the differences between dominant and recessive traits. Also included is the student exploration sheet (which I have modified slightly for my students), the Teacher's Guide, and the vocabulary sheet. I have also included the original lesson plan with this activity embedded as the "Independent Practice" section.

http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=382&ClassID=1701917